What Are The Methods For Adjusting The Flow Rate Of A Centrifugal Pump?

Mar 01, 2025

Chemical centrifugal pumps are commonly used in various industries. Centrifugal pumps are used in industries such as water conservancy and chemical engineering. The selection of operating points and energy consumption analysis are also receiving increasing attention. The so-called working point refers to the instantaneous actual water output, head, shaft power, efficiency, and vacuum suction height of the chemical centrifugal pump device. It represents the working capacity of the centrifugal pump. Usually, the flow rate and pressure head of a centrifugal pump may not be consistent with the pipeline system, or the flow rate of the pump may need to be adjusted due to changes in production tasks and process requirements. Its essence is to change the operating point of the centrifugal pump. When users choose centrifugal pumps, they often determine the flow rate based on actual usage. Each model of water pump has a standard flow rate. For pumps that cannot reach the standard flow rate of the pump type, what are the methods for adjusting the flow rate of centrifugal pumps, and what methods can be used to meet the requirements?

1.Valve throttling
A simple method to change the flow rate of a chemical pump is to adjust the opening of the pump outlet valve while keeping the pump speed constant (usually the rated speed). Its essence is to change the position of the pipeline characteristic curve to alter the working point of the pump. When the valve is closed, the local resistance of the pipeline increases, the working point of the pump moves to the left, and the corresponding flow rate decreases. When the valve is completely closed, it is equivalent to infinite resistance and zero flow, and the characteristic curve of the pipeline is consistent with the vertical axis. When the valve is closed to control the flow rate, the water supply capacity of the pump itself will not change, the lifting characteristics will not change, and the pipeline resistance characteristics will change with the change of valve opening. This method is easy to operate, with continuous flow, and can be adjusted freely between a large flow and zero without additional investment. It is suitable for many occasions.
2.Cutting impeller
When the speed is constant, the pressure head and flow rate of the pump are related to the diameter of the impeller. For pumps of the same model, cutting method can be used to change the characteristic curve of the pump. The cutting law is based on a large amount of sensory experimental data. It holds that if the cutting amount of the impeller is controlled within a certain limit (which is related to the specific speed of the water pump), the corresponding efficiency of the water pump before and after cutting can be regarded as constant. Cutting impellers is a simple and feasible way to change the performance of water pumps, also known as variable diameter adjustment. It solves the contradiction between the limited types and specifications of water pumps and the diversity of water supply requirements to a certain extent, and expands the scope of use of water pumps. Of course, cutting impellers is an irreversible process, and users must undergo precise calculations and measure economic rationality before implementation.
3. frequency control
The deviation of the operating point from the high-efficiency zone is a basic condition for the speed regulation of the water pump. When the speed of the water pump changes, the valve opening remains unchanged (usually a large opening), the pipeline system characteristics remain unchanged, but the water supply capacity and head characteristics change accordingly.
When the required flow rate is less than the rated flow rate, the head during variable frequency speed regulation is smaller than that of valve throttling, so the water supply power required for variable frequency speed regulation is also smaller than that of valve throttling. Obviously, compared with valve throttling, the energy-saving effect of variable frequency speed regulation is outstanding, and the working efficiency of centrifugal pumps is higher. In addition, adopting variable frequency speed regulation not only helps to reduce the possibility of cavitation in centrifugal pumps, but also extends the start-up/shutdown process by presetting the speed increase/decrease time, greatly reducing the dynamic torque and greatly reducing the destructive water hammer effect, greatly extending the life of the water pump and pipeline system. In fact, variable frequency speed regulation also has limitations. In addition to high investment and maintenance costs, when the water pump changes speed too much, it will cause a decrease in efficiency, exceeding the range of the pump proportional law and making speed regulation impossible.